To solve one that has three variables, generally speaking, we need to have three equations (that are different from each other.)
Our goal is to combine two of the equations and eliminate a single variable, or, if you get really lucky, two variables.
There's not really a prescribed way to proceed - and there's really not a wrong way to proceed on these either. Your goal is to isolate and substitute - and eliminate as much as possible in each step.
If you'll post a specific question on this, I can help you solve it, though - or walk you through the process and the reasoning behind the different steps..